The field of the invention pertains to motor vehicle exhaust catalytic converters and, in particular, to the detection of the failure of such catalytic converters during normal vehicle operation.
To address air quality problems in our most polluted cities, those charged with the responsibility to clean up the air are increasingly concerned with in-use motor vehicle emissions in addition to new car compliance programs. One of the most visible programs is the inspection and maintenance program now enforced in a number of populated regions of the United States. As vehicle technology has become more sophisticated, the use of the vehicles' electronic control system to identify its own malfunctions has become a viable strategy for supplementing or enhancing traditional inspection and maintenance programs.
Until recently no need for on-board exhaust emissions diagnostics technology was exhibited because no requirements were coming into force. Motor vehicle on-board diagnostic monitoring systems were first required in the State of California beginning in the 1988 model year. The first generation system, monitoring only exhaust gas recirculation and fuel system performance, had limited diagnostic capabilities. Recognizing that malfunctions of other vehicle emissions control systems such as the secondary air system, evaporative control system, and the catalytic converter can also significantly affect motor vehicle emissions, the State of California adopted second generation on-board diagnostic system requirements applicable to 1994 and later model year vehicles.
Concurrent with the State of California regulations, the U.S. Environmental Protection Agency initiated the development of Federal on-board diagnostic regulations. The recently enacted Clean Air Act Amendments of 1990 specifically require the monitoring of catalysts and oxygen sensors in the exhaust stream by the on-board diagnostic system.
The use of a post-catalyst oxygen sensor is known from a study published in 1980 by A. H. Meitzler, Society of Automotive Engineers (SAE paper 800019). The response delay of a downstream oxygen sensor to an instantaneous air/fuel shift is used as an indicator of an exhaust catalyst's oxygen storage mechanisms. In more recent years, at least one automotive manufacturer has used a downstream oxygen sensor (in combination with an upstream sensor) in a limited capacity as part of the vehicle's fuel control feedback loop.